Cast steel connections appear more frequently in contemporary structural steel as designers pursue geometry that rolled and built-up shapes cannot achieve. Column base plates cast as a single node, moment connection brackets, space-frame nodes, and architecturally exposed structural steel (AESS) elements in complex assemblies are all applications where ASTM A216 WCB (carbon steel, weldable grade), A27 (general-use structural casting), or A148 (high-strength structural) cast steel shows up in a fabrication shop's work order.

The first thing any CWI or QC manager needs to know about cast steel: it is not on the AWS D1.1 prequalified base metal list. This is not a paperwork distinction—it means the fabricator cannot write a prequalified WPS for any joint that includes cast steel. Every welding procedure for a cast steel weldment must be supported by a qualification test plate, a PQR, and tested mechanical properties before production welding begins.

Why Cast Steel Requires a Tested WPS

AWS D1.1's prequalified WPS provisions apply to base metals that AWS has validated for weldability within the prequalified parameter limits. The prequalified base metal list covers wrought structural plate and shapes: A36, A572, A588, A913, A992, and comparable grades—materials produced by hot rolling or forging with a controlled, uniform microstructure.

Cast steel is excluded because the as-cast microstructure is inherently more variable than wrought plate:

  • Grain size is larger and less uniform in castings than in hot-rolled or normalized plate, reducing toughness in the heat-affected zone
  • Solidification segregation during casting can produce local variations in carbon, manganese, and sulfur content that raise the effective carbon equivalent above what the heat analysis shows
  • Internal shrinkage and porosity are possible in cast sections and affect weld soundness at the fusion line
  • Surface condition on as-cast faces—oxide scale, inclusions, and surface porosity—requires more aggressive pre-weld preparation than mill-scale removal on wrought plate

None of these factors makes cast steel unweldable. They make it a material with known variability that requires procedure qualification to demonstrate sound welds under your specific shop conditions, with your specific base material lot.

PQR Path for Cast Steel Weldments

The PQR for a cast steel weldment follows the same sequence as for wrought steel groove welds: qualify a test plate that matches the proposed production joint in base metals, joint geometry, position, and process; run the required mechanical tests; and document everything in a formal PQR.

Test material procurement: The qualification test plates must use the actual production material. For A216 WCB, the PQR base metal is WCB casting material, not A36 plate. If the production joint is a T-butt of A572 Grade 50 plate to A216 WCB casting, both materials must be represented in the test assembly. Substituting wrought plate for the casting because it is easier to obtain produces a PQR that does not support the production joint—and an experienced auditor will catch it immediately.

Mechanical test requirements: The test plate must yield tensile specimens (reduced section or longitudinal), guided bend specimens (root and face or side depending on thickness), and—where CVN testing is required by the project—Charpy impact specimens from the weld metal and HAZ. Hardness testing is frequently added in project specifications for cast steel joints because the as-cast HAZ can harden above anticipated levels, particularly in WCB heats on the high end of the specified carbon range.

Position coverage: Qualify in the positions required for production. Cast steel nodes in AESS structures or architectural features often require inclined or overhead position welding that must be explicitly covered by the PQR positions. A PQR tested flat and horizontal does not cover overhead production welds to the same casting.

See how to qualify a welding procedure under AWS D1.1 for the general qualification test sequence and the position coverage rules.

Filler Metal Selection

For welding A216 WCB or A27 Grade N-2 (normalized) cast steel to common structural grades (A36, A572 Grade 50), low-hydrogen electrodes at the E70 tensile level satisfy the joint requirements:

  • SMAW: E7018-H4 or E7018-H8 — the H4 diffusible hydrogen limit (4 mL/100g deposited weld metal) is preferred when the casting has a CE approaching 0.45 or when preheat is below 300°F; H8 is the minimum acceptable for most structural cast steel applications
  • FCAW-G: E71T-1C or E71T-12C with CO₂ or 75/25 Ar/CO₂ shielding gas
  • GMAW: ER70S-3 or ER70S-6 (ER70S-6 preferred for castings with surface oxide scale that may not be fully removed)
  • SAW: F7A4-EM12K or equivalent with appropriate flux classification

The H-suffix matters more for cast steel than for wrought plate. The coarser HAZ grain structure in castings increases susceptibility to hydrogen-assisted cold cracking in the days following welding—sometimes referred to as underbead cracking or delayed cracking. Low-hydrogen practice (low-hydrogen electrode, moisture control, preheat maintenance, and adequate interpass temperature) is non-negotiable for cast steel weld joints. See electrode H-suffix classification and WPS documentation for the diffusible hydrogen limits and their code basis.

For A148 Grade 80-40 or higher-strength cast steels, the filler metal tensile strength requirement increases. E8018-C3 or ER80S-D2 may be required. The PQR tensile tests establish the minimum tensile strength the weld metal must achieve; the WPS filler metal specification must document a classification that meets it.

Preheat and Interpass Temperature for Cast Steel

AWS D1.1 does not publish prequalified preheat values for cast steel. Preheat is determined from the casting's actual carbon equivalent, documented on the certified material test report (CMTR), and recorded in the WPS.

Preheat determination for cast steel:

  1. Obtain the CMTR for the casting heat and confirm it covers the chemical composition (C, Mn, Si, P, S, Cr, Ni, Mo, V minimally)
  2. Calculate the carbon equivalent using the CE formula applied throughout AWS D1.1: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
  3. Apply preheat based on CE and section thickness, treating cast steel conservatively—add 25°F to 50°F versus wrought plate at the same CE to account for segregation effects and grain size
  4. Document the preheat temperature, measurement method, and minimum soak time in the WPS

For A216 WCB in common structural thicknesses (1 to 3 inches), preheat values of 200°F to 350°F are typical. For heavy-section castings (>3 inches), preheat of 300°F to 400°F with controlled post-weld cooling is not unusual. After welding, the assembly should be slow-cooled by insulation blankets—rapid air cooling from elevated preheat temperatures can create steep temperature gradients in thick cast sections and increase residual stress.

Interpass temperature maximum for A216 WCB is typically held at 450°F to 500°F. Exceeding this during fill passes softens the weld metal and can reduce CVN impact values if notch toughness is required.

See preheat and interpass temperature on a WPS for documentation requirements and inspection verification procedures.

Surface Preparation and Fit-Up

Cast steel surfaces present challenges that rolled plate does not:

As-cast scale and inclusions: The surface of a structural casting as received is rough and oxide-covered. All as-cast scale must be removed by grinding or abrasive blast cleaning before welding. Surface-connected casting defects—sand inclusions, cold shuts, or porosity at the weld zone—must be identified during pre-weld inspection.

Subsurface casting defects in the weld zone: Before making the structural weld, MT or PT the casting surface in the weld zone. If casting porosity, shrinkage voids, or inclusions are found, excavate them by grinding until sound metal is reached, confirm soundness by MT, and fill with a documented repair weld before making the structural joint. Welding over existing casting defects does not heal them—it embeds them at the fusion line where they are most dangerous.

Dimensional variation: Cast steel components have more dimensional tolerance variation than machined or rolled plate. Root opening and joint fit-up in cast-to-plate connections may be wider than nominal, and the WPS must accommodate the actual fit-up achievable in production. If the root opening exceeds the WPS-qualified range, a documented deviation procedure is required before welding.

NDE for Cast Steel Welds

UT can be challenging on cast steel. The coarse, anisotropic grain structure creates acoustic scattering that elevates background noise and can mask real discontinuities. UT still has a role for detecting large internal defects, but its sensitivity for small, tight flaws in the cast grain structure is reduced compared to wrought plate.

For critical cast steel weld joints—structural nodes in AESS buildings, column-base moment connections, transfer structure elements—radiographic testing (RT) is often specified as the primary volumetric NDE method. RT provides a clear image of weld metal porosity, slag inclusions, and casting defects at the weld interface without the grain-noise limitations of UT. RT films or digital radiographs also provide a permanent visual record that can be reviewed by a third party without re-inspecting the weld.

MT is the standard surface NDE method for cast steel welds. Apply MT:

  • After pre-weld preparation (confirm casting surface is defect-free before welding)
  • After completing the structural weld (detect surface and near-surface cracks in weld metal and HAZ)
  • After any weld repair

PT is an alternative to MT for non-ferromagnetic grades, though carbon cast steels are magnetic and MT is preferred. See NDE documentation for the audit packet for record-keeping requirements.

What the Weld Package Needs for Cast Steel Joints

A complete weld package for a cast steel weldment includes:

  • Casting CMTR: heat chemical analysis, mechanical test results (tensile, Charpy if specified), heat treatment certification (normalized, normalized and tempered, or as-cast), and the pour date
  • WPS with explicit call-out of the ASTM casting grade (A216 WCB, A27, or A148 as applicable) as the base metal—"structural steel" is not sufficient
  • PQR showing mechanical test results for the applicable cast-to-wrought or cast-to-cast joint combination
  • Welder WPQ covering the applicable process and position, with qualification date and continuity record
  • Pre-weld inspection report: surface prep acceptance, casting defect evaluation and repair if any, preheat verification before first pass
  • Production weld records: interpass temperature checks, electrode heat/lot identification, parameter log if CVN testing is required
  • NDE reports: RT films or digital files, MT records, all tied to the specific weld location on the weld map

The CMTR for the casting is frequently missing in audit situations—shops obtain the casting, weld it, and never retain the CMTR as part of the weld package. Without the CMTR, there is no basis for the preheat temperature specified in the WPS, and the traceability chain breaks.

If your shop handles recurring cast steel work, building a dedicated WPS in your WPS library for each casting-to-wrought combination avoids re-qualifying the procedure for every project. Managing cast steel WPS documents alongside your standard structural WPS library is straightforward with software that supports multiple base metal combinations; see our pricing page for plans that include the full WPS and PQR document management suite.